Scour and flow field around a spur dike in a 90° bend

Spur dike is an important element in fiver training that creates rapid variations in flow field, sediment transport and bed topography. The mechanism of flow and sediment transport in a channel bend is very complex, especially when a spur dike is constructed in a bend. Most of previous investigations on flow behavior and scour around spur dike were carried out in straight channels. In this paper results of experiments on flow field and scour around a spur dike in a 90 degree channel bend are presented, Sand with uniform grain size was used as the bed material, Experiments were conducted for different locations and different lengths of spur dikes at the bend with different values of discharge, The three dimensional flow fields around a spur dike were investigated, The maximum depth of scour was correlated to the Froude numbers, lengths and the locations of spur dike in the bend.     

Effects of bed perturbation and velocity asymmetry on ripple initiation: wave-flume experiments

Laboratory experiments using a wave flume were designed to examine the threshold condition for ripple formation under asymmetrical oscillatory flows on an artificially roughened bed. Three types of sand beds were prepared in the experiments: they were flat, notched, and notch-mounded beds with bed roughness increasing in this order. The beds were constructed with three kinds of well-sorted sand with similar density, but different diameters. Data analyses were made using the two dimensionless parameters: the mobility number, M, a simplified form of the Shields number, and the Ursell number, U, a surrogate for asymmetry of flow field. The result confirmed that the threshold for ripple initiation is decreased with increasing bed perturbation and that as the bed perturbation increases, the dependency of this threshold on the flow asymmetry becomes less and finally null for the notch-mounded bed. This relationship is quantified by the following equations: M=17−14.5e^−0.03U on the flat bed, M=5.0−2.5e^−0.1U for the notched bed, and M=2.5 for the notch-mounded bed. A comparison between the previous field data and the present laboratory findings indicates that the threshold in the notch-mounded bed experiment, M=2.5, seems to provide a critical condition for rippling in the natural environment.     

滇西北三叠系铅锌铁铜多金属矿含矿层位

滇西北德钦—维西一带有一类重要的铁铜铅锌多金属矿,含矿岩石为一套夹中酸性—基性火山岩的沉积岩系。目前的地质文献中,该沉积岩系的时代和名称争论颇多。笔者研究后认为应是中三叠统攀天阁组、中—上三叠统崔衣比组。建议以巍山地区歪古村组、三合洞组、挖鲁八组及麦初箐组作为兰坪—思茅中、新生代上叠陆内盆地的上三叠统地层名称;而攀天阁组、崔衣比组及石钟山组则为金沙江构造带维西陆缘弧带的三叠系地层名称,便于两个不同大地构造单元三叠系地层的对比。     

EFFECTS OF SEDIMENT GRADATION ON THE GEOMETRY OF RIVER DELTAS

l INTRODUCTlONIn this study, formation of alluvial deltas was treated as a river-dominated type of topograPhy process,caused simply by sediment deposition from a channel into a wide basin. The influences of waves, tides,and density differences related to coastal effects were excluded. There have been numerous experimentalstUdies on river delta problems. For examPle, Shieh et al. (1988, 1997) used coarse sediment asexperimental material and revealed the development and the geometric simil…     

Numerical Simulation of Bed Separation Development and Grout Injecting into Separations

In this paper, the Cosserat theory that has been incorporated into a three dimensional finite element code COSFLOW, is applied to analyze the development of bed separations in the layered overburden and grout injection into the bed separations. The mechanism of bed separation development during the longwall mining is investigated. A parametric study is carried out to investigate the effect of major factors including hard rock grade, panel height and panel weight on bed separation development. Based on the modeling, a conceptual model to describe the development process of bed separation is proposed. The effect of grout injecting into the bed separations on subsidence reduction is also studied and the conclusion agrees well with the common realization.     

Filtrate Quality from Different Filter Operations

A brief review of the literature on filtrate quality obtained in constant and variable declining rate operation systems is presented, with the general conclusion that both systems usually produce filtrate of similar quality, assuming the flow‐rate controllers in the constant flow rate system operate properly. A mathematical model of CR (constant rate) filters and VDR (variable declining rate) filters based on the model by Mackie and Zhao (1999) has been described and used to investigate filtrate quality under different operating conditions. A similar quality of filtrate was achieved in computations carried out for both modes of operation, while the total head loss was much lower in the VDR mode. For the same time of filter runs slightly better filtration quality resulted from CR operation, but for different filter runs resulting from the same head loss of flow just before a backwash, the VDR control system produced lower turbidity filtrate.     

Adaptive adjustment of channel geometry

This paper constructs a model of channel geometry composed of three subsections: a steady-state submodel, a gradedstate submodel, and a stochastic error submodel. With the aid of this representation of the morphology of channels, the at-a-point changes in geometry can be reproduced by a simple recursive equation of autoregressive, moving-average form which is derived from methods used in the statistical analysis of time series. A set of height loss data for three Japanese rivers derived from Yatsu's (1955) paper is used to determine the effect of bed material changes on adaptations within the graded-state submodel of the channel. The results of analyzing the autocorrelation function, spectrum, and adaptive parameter shifts within this model can be used to infer that significant changes in the amplitude of height change variation, and a shift to higher frequency oscillations of bed forms are associated with the shift in bed material conditions.     

云南麻栗坡芭蕉箐铅锌矿成因探讨

矿体似层状、透镜状赋存于中寒武系田蓬组碳酸盐岩岩系中,北东向褶皱的滑脱空间、断裂破碎带为容矿的重要场所。     

老挝琅勃拉邦爬奔金矿矿床地质及成因探讨

琅勃拉邦省位于“三江”成矿带南延部分,爬奔金矿为受剪切带控制的低温热液矿床,矿体产出空间符合里德尔剪切裂隙规律,进一步工作后该矿区应有中型以上规模。